I don't know much about racing games, and my predictions shouldn't be worth much, but I'll do it anyway.
Forza Horizon will probably suffer being cross-gen, and sering how the main series entry scored, i say 79.
Driveclub, on the other hand, seems like a very promising game, and will be another of many 90+ scoring PS4 games - 92.
Project CARS will probably score dome extra points being an indie game - 83.
Also, there is The Crew that wasn't mentioned. Actually a racing game I find interesting in concept - racing across the USA instead of in an endless circle. The only game I actually consider playing down the line. But it probably won't be that great - 81.